Ministry of Aircraft Production tried to find isolated area for trials in 1943 but had to postpone plan as rainy season approached

Britain planned to test a very virulent type of poison gas in what is now Botswana, the colonial archives reveal.

The plan for “practical trials” carried out on a “considerable scale” was first proposed by the Ministry of Aircraft Production in 1943. It was looking for an “isolated area” of about 10 sq miles that was free of people, Britain’s high commission in Pretoria was told.

The Pretoria government quickly told the British that there was no suitable area within the Union of South Africa, according to the hitherto secret file marked “FORENSIC”, the codename given to the planned operation.

British officials then suggested that the Makarikari region of Bechuanaland would be suitable as a “chemical experimental area”. But facilities there were regarded as being too small. Moreover, one official noted, there was another disadvantage, namely “the presence of game including lions”.

The British turned their attention to the Makgadikgadi Pan, a large salt pan to the north of the then British protectorate. It would be preferable, they said, if at least some of the land chosen for poison gas experiments there was owned by the British crown.

In July 1943 a clearly nervous – and unidentified – British colonial official wrote to the UK ministry that was asking for a site to test its gas: “Your instructions have been noted and your letter destroyed by burning.”

An area south of Nata lake, to the east of the country, was chosen as being “eminently suitable” for the tests as there was no water within 15 miles, British officials noted. But by November 1943 they had still not decided where to test the poison gas. The trials were postponed “due to the proximity of the rainy season”, an official noted. So the plan would be postponed until the following year.

This is the last note in the file and it is likely that the plan never went ahead.

Files released on Wednesday show British officials were nervous in the years before the second world war about the activities of Italians and Japanese in east Africa, recording shipping movements and safari trips in intelligence reports and even suspecting Germans catching butterflies in Kenya of being Nazi agents.

A monthly intelligence report from the Kenyan port of Mombasa in August 1938 noted that a German, Herr Stieglitz, a representative of the tyre manufacturer Continental, had recently been on two safaris, on one of which he had killed a buffalo.

It continues: “Contact remarked that he would not like to be within range of a rifle in the hands of this person, whom he described as being a ‘crack shot’. He also stated that the Germans who visit Kisigau usually shoot something.”

The document records a drunken Italian ship’s officer telling a source that he had heard Germans say they could organise a “semi-trained force of about 5,000 men” in east Africa if hostilities broke out.